Issue 55

A.V. Chernov et alii, Frattura ed Integrità Strutturale, 55 (2021) 174-186; DOI: 10.3221/IGF-ESIS.55.13

simultaneous measurements of deformation response, caused by local material removing, on both specimen faces have to be involved. A set of required experiments is currently under consideration. The results obtained will be reported later.

a

b

Figure 7: Residual SIF  n

I K values as a function of loading cycle number N for T5-H1 (a) and T5-H2 (b) specimens for notches of

length  n a (n =1, 2, 3). Data, presented in Fig.6b, provide a way to derive SIF values, connected with residual stress only, by means of technique proposed in work [11]. The essence of this approach resides in implementing the linear superposition principal in order to evaluate SIF values   n RS I K , which are related to pure residual stress field. In other words,   n RS I K can be presented as the difference in experimental SIF value  n I K and theoretical (numerical) SIF value nT I K , which are obtained for specimens of equal geometry with the same crack length under the same remote stress:       n RS n nT I I I K K K (2)

  1 RS

1 T I K are listed in Tab. 4. This table also includes

I K

values obtained by

where n =1, 2, 3. Theoretical SIF values

relationship (2) for notch of  1 a length proceeding from experimental data shown in Fig. 6b.

  1 RS

 n I K ,

1 T I K ,

 1 a , mm

σ , MPa

 MPa m

 MPa m

 MPa m

I K

,

60 80

2.52 2.30 2.43

− 5.1 − 2.6

7.4

− 12.50 − 12.26 − 12.20

9.66 12.2

100

0

Table 4: SIF values for different remote stress levels. Data of Tab. 4 demonstrate that residual SIF values, calculated for different remote stress levels, coincide within 2.4 percent. This fact provides reason enough to implement linear fracture mechanics relations in the course of experimental SIF determination when a crack length met to the condition   1 a 2 mm. Thus, Formula (1) can be reliably used for residual SIF   n RS I K determination for all three notches of different length, emanating from cold-expanded holes at different stages of low-cycle fatigue. Dependencies of residual SIF values from number of loading cycle are shown in Fig. 8a and 8b for specimens of T5-H1 and T5-H2 group, respectively.

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